Kinetics and mechanisms of the oxidation of methyl aryl ketones by acid permanganate

1976 ◽  
Vol 29 (9) ◽  
pp. 1939 ◽  
Author(s):  
MP Nath ◽  
KK Banerji
Keyword(s):  
Isotope Effect ◽  
Reaction Rate ◽  
Activation Parameters ◽  
Hydrogen Ions ◽  
Solvent Isotope Effect ◽  
Fluoride Ions ◽  
First Order ◽  
Kinetic Isotope ◽  
Aryl Ketones ◽  
Solvent Isotope

The oxidation of six methyl aryl ketones by acid permanganate has been studied, in the presence of fluoride ions. The products of the oxidation are formaldehyde and the corresponding benzoic acids.The oxidation is first order with respect to each the ketone, the oxidant and hydrogen ions. The reaction rate increases sharply with the increase in the amount of acetic acid in the solvent. The oxidation of acetophenone exhibits the kinetic isotope effect, kH/kD = 4.60 at 30�C. The solvent isotope effect is given by k(D2O)/k(H2O) = 5.03. The acid-catalysed enolization rate of the ketones has been measured by the bromination method. The activation parameters for both the oxidationand enolization reactions have been evaluated. The oxidation is slower than the acid-catalysed enolization. The relative rates of the oxidation are proportional to the relative rates of enolization.These results coupled with the magnitude of the solvent isotope effect suggest that the enol form of the ketone is involved in the oxidation process. A possible mechanism has been suggested.

Kinetics and Mechanism of the Oxidation of Some α-Hydroxyacids by Morpholinium Chlorochromate

2008 ◽  
Vol 33 (4) ◽  
pp. 393-405
Author(s):  
Neha Malani ◽  
Manju Baghmar ◽  
Preeti Swami ◽  
Pradeep Kumar Sharma
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Ion Transfer ◽  
Hydrogen Ions ◽  
Solvent Isotope Effect ◽  
First Order ◽  
Hydride Ion ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Hydride Ion Transfer

The oxidation of glycollic, lactic, malic and a few substituted mandelic acids by morpholinium chlorochromate (MCC) in dimethylsulfoxide (DMSO) leads to the corresponding oxoacids. The reaction is first order each in MCC and hydroxyacid. The reaction failed to induce the polymerisation of acrylonitrile. The oxidation of α–deuteriomandelic acid shows a primary kinetic isotope effect ( kH/ kD = 5.63 at 298 K) but does not exhibit a solvent isotope effect. The reaction is catalysed by hydrogen ions according to: kobs = a + b[H+]. The oxidation of p-methyl mandelic acid has been studied in 19 different organic solvents and the solvent effect analysed using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed.

scholarly journals Kinetics and Mechanism of the Oxidation of α-Hydroxy Carboxylic Acids by Bromine

1973 ◽  
Vol 28 (7-8) ◽  
pp. 450-453 ◽  
Author(s):  
Kalyan K. Banerji
Keyword(s):  
Isotope Effect ◽  
Hydroxy Acid ◽  
Kinetic Isotope Effect ◽  
Activation Parameters ◽  
Probable Mechanism ◽  
Molecular Bromine ◽  
Solvent Isotope Effect ◽  
First Order ◽  
Kinetic Isotope ◽  
Solvent Isotope

The oxidation of glycollic, lactic, u-hydroxybutyric, and 2-phenyllactic acids by aqueous bromine has been studied. The reaction is of first order with respect to the oxidant and the anion of the hydroxy acid respectively. The active oxidising species is molecular bromine. The oxidation of α,α-dideuterioglycollic acid indicated a kinetic isotope effect, kH/kD=4.62 at 25°C. The reaction does not show any appreciable solvent isotope effect. The activation parameters arc evaluated. A probable mechanism has been suggested.

scholarly journals Kinetics and mechanism of the oxidation of substituted benzyl alcohols by sodium N-bromobenzenesulfonamide

1985 ◽  
Vol 63 (10) ◽  
pp. 2726-2729 ◽  
Author(s):  
Seema Kothari ◽  
Kalyan Kumar Banerji
Keyword(s):  
Isotope Effect ◽  
Activation Parameters ◽  
Hydrogen Ions ◽  
Solvent Isotope Effect ◽  
Benzyl Alcohols ◽  
Rate Determining Step ◽  
Kinetic Isotope ◽  
Reaction Constant ◽  
Different Temperatures ◽  
Solvent Isotope

The oxidation of substituted benzyl alcohols by sodium N-bromobenzenesulfonamide (BAB) in acid solution results in the formation of the corresponding benzaldehydes. The reaction is first order with respect to BAB, the alcohol, and hydrogen ions. The reaction exhibits a primary kinetic isotope effect (kH/kD = 5.26). The value of the solvent isotope effect, k(H2O)/k(D2O), equals 0.43 at 298 K. Addition of benzenesulfonamide has no effect on the rate. Increase in amount of acetic acid in the solvent increases the rate. The reaction rate has been determined at five different temperatures and the activation parameters have been calculated. (PhSO2NH2Br)+ has been postulated as the reactive oxidizing species. The rates of oxidation of substituted benzyl alcohols correlate very well with Brown's σ+ constants. The value of the reaction constant is −2.84 at 298 K. A hydride transfer from the alcohol to the oxidant, in the rate-determining step, has been proposed.

scholarly journals The β-glucosidase from Botryodiplodia theobromae. Mechanism of enzyme action

1981 ◽  
Vol 199 (1) ◽  
pp. 203-209 ◽  
Author(s):  
G M Umezurike
Keyword(s):  
Isotope Effect ◽  
Maximum Velocity ◽  
Competitive Inhibitor ◽  
Ion Pair ◽  
High Concentration ◽  
Botryodiplodia Theobromae ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Beta Glucosidase ◽  
Solvent Isotope

1. In the presence of a high concentration of p-nitrophenyl beta-D-glucopyranoside (donor) the rates of production of p-nitrophenol and a transglucosylation product (1-glyceryl beta-D-glucopyranoside) increased, whereas the rate of production of glucose decreased with increasing concentration of glycerol in reactions catalysed by the high-molecular-weight beta-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) obtained from culture filtrates of Botryodiplodia theobromae Pat. 2. When [donor] greater than Km the rate of production of p-nitrophenol was higher in the presence of glycerol than in its absence, whereas when [donor] less than Km the rate of production of p-nitrophenol was lower in the presence of glycerol than in its absence. 3. Glycerol increased both the Michaelis constant (Km) and maximum velocity (Vmax.), whereas dioxan increased Km but decreased Vmax. 4. Up to 1 mM-AgNO3 had no effect on enzyme activity. 5. A 2H-solvent-isotope-effect [Vmax. (H2O)/V max. (2H2O)] value of 1.40 +/- 0.05 was found at pH (or p2H) 5.8 6. alpha-2H-kinetic isotope-effect (kappa H/kappa 2H) values of 1.03 +/- 0.01 and 1.05 +/- 0.01 were found in the absence and presence of glycerol respectively. 7. Although maltose was a non-competitive inhibitor of beta-glucosidase activity, the ratio of velocity in the presence of glycerol to that in its absence increased, after an initial decline, with increasing concentration of maltose. 8. These results are discussed in terms of a mechanism involving a solvent-separated glucosyl cation-carboxylate ion-pair, which has greater affinity for alcoholic glucosyl acceptors, and an intimate ion-pair, which has greater affinity for water as a glucosyl acceptor and which could collapse reversibly and rapidly into a preponderance of an unreactive covalent glucosyl-enzyme.

scholarly journals Inverse Solvent Isotope Effects in Enzyme-Catalyzed Reactions

Molecules ◽  
2020 ◽  
Vol 25 (8) ◽  
pp. 1933
Author(s):  
Patrick L. Fernandez ◽  
Andrew S. Murkin
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Catalyzed Reactions ◽  
Enzyme Catalyzed Reactions ◽  
Solvent Isotope ◽  
Rate Limiting ◽  
Solvent Isotope Effects

Solvent isotope effects have long been used as a mechanistic tool for determining enzyme mechanisms. Most commonly, macroscopic rate constants such as kcat and kcat/Km are found to decrease when the reaction is performed in D2O for a variety of reasons including the transfer of protons. Under certain circumstances, these constants are found to increase, in what is termed an inverse solvent kinetic isotope effect (SKIE), which can be a diagnostic mechanistic feature. Generally, these phenomena can be attributed to an inverse solvent equilibrium isotope effect on a rapid equilibrium preceding the rate-limiting step(s). This review surveys inverse SKIEs in enzyme-catalyzed reactions by assessing their underlying origins in common mechanistic themes. Case studies for each category are presented, and the mechanistic implications are put into context. It is hoped that readers may find the illustrative examples valuable in planning and interpreting solvent isotope effect experiments.

Kinetics and Mechanism for the Hydrolysis of Chlorothionoformate and Chlorodithioformate Esters in Water and Aqueous Acetone

1972 ◽  
Vol 50 (9) ◽  
pp. 1401-1406 ◽  
Author(s):  
D. M. McKinnon ◽  
A. Queen
Keyword(s):  
Isotope Effect ◽  
Structural Changes ◽  
Activation Parameters ◽  
Aqueous Acetone ◽  
Kinetics And Mechanism ◽  
Solvent Isotope Effect ◽  
Hydrocarbon Group ◽  
Solvent Isotope ◽  
Electron Donation ◽  
Hydrolysis Of

The effects of structural changes on the rates of hydrolysis of a series of chlorothionoformate esters and the analogous chlorodithioformate esters have been studied. For both classes of compound, the reactivity is enhanced by increased electron donation by the hydrocarbon group. These results, the activation parameters for the hydrolyses of the methyl compounds, and the solvent isotope effect are shown to be consistent with the operation of the SN1 mechanism.

scholarly journals A solvent-isotope-effect study of proton transfer during catalysis by Escherichia coli (lacZ) β-galactosidase

1990 ◽  
Vol 268 (2) ◽  
pp. 317-323 ◽  
Author(s):  
T Selwood ◽  
M L Sinnott
Keyword(s):  
Escherichia Coli ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Effect Study ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Paper Abstract ◽  
Hydrolysis Of

1. Michaelis-Menten parameters for the hydrolysis of 4-nitrophenyl β-D-galactopyranoside and 3,4-dinitrophenyl β-D-galactopyranoside Escherichia coli (lacZ) β-galactosidase were measured as a function of pH or pD (pL) in both 1H2O and 2H2O. 2. For hydrolysis of 4-nitrophenyl β-D-galactopyranoside by Mg2(+)-free enzyme, V is pL-independent below pL 9, but the V/Km-pL profile is sigmoid, the pK values shifting from 7.6 +/- 0.1 in 1H2O to 8.2 +/- 0.1 in 2H2O, and solvent kinetic isotope effects are negligible, in accord with the proposal [Sinnott, Withers & Viratelle (1978) Biochem. J. 175, 539-546] that glycone-aglycone fission without acid catalysis governs both V and V/Km. 3. V for hydrolysis of 4-nitrophenyl β-D-galactopyranoside by Mg2(+)-enzyme varies sigmoidally with pL, the pK value shifting from 9.19 +/- 0.09 to 9.70 +/- 0.07; V/Km shows both a low-pL fall, probably due to competition between Mg2+ and protons [Tenu, Viratelle, Garnier & Yon (1971) Eur. J. Biochem. 20, 363-370], and a high-pL fall, governed by a pK that shifts from 8.33 +/- 0.08 to 8.83 +/- 0.08. There is a negligible solvent kinetic isotope effect on V/Km, but one of 1.7 on V, which a linear proton inventory shows to arise from one transferred proton. 4. The variation of V and V/Km with pL is sigmoid for hydrolysis of 3,4-dinitrophenyl β-D-galactopyranoside by Mg2(+)-enzyme, with pK values showing small shifts, from 8.78 +/- 0.09 to 8.65 +/- 0.08 and from 8.7 +/- 0.1 to 8.9 +/- 0.1 respectively. There is no solvent isotope effect on V or V/Km for 3,4-dinitrophenyl β-D-galactopyranoside, despite hydrolysis of the galactosyl-enzyme intermediate governing V. 5. Identification of the ‘conformation change’ in the hydrolysis of aryl galactosides proposed by Sinnott & Souchard [(1973) Biochem. J. 133, 89-98] with the protolysis of the magnesium phenoxide arising from the action of enzyme-bound Mg2+ as an electrophilic catalyst rationalizes these data and also resolves the conflict between the proposals and the 18O kinetic-isotope-effect data reported by Rosenberg & Kirsch [(1981) Biochemistry 20, 3189-3196]. It should be noted that the actual Km values were determined to higher precision than can be estimated from the Figures in this paper.(ABSTRACT TRUNCATED AT 400 WORDS)

Kinetic and solvent isotope effects in oxidation of halogen derivatives of tyramine catalyzed by monoamine oxidase A

2019 ◽  
Vol 167 (1) ◽  
pp. 49-54
Author(s):  
Małgorzata Pająk
Keyword(s):  
Monoamine Oxidase ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Monoamine Oxidase A ◽  
Oxidative Deamination ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Derivatives Of ◽  
Solvent Isotope Effects

Abstract The isotope effects approach was used to elucidate the mechanism of oxidative deamination of 3′-halotyramines, catalyzed by monoamine oxidase A (EC 1.4.3.4). The numerical values of kinetic isotope effect (KIE) and solvent isotope effect (SIE) were established using a non-competitive spectrophotometric technique. Based upon KIE and SIE values, some of the mechanistic details of investigated reaction were discussed.

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